The differentiation and development processes are of particular importance in the intestine because its epithelium is continually undergoing a renewal process throughout life. The nature of the molecular mechanisms that underlie intestinal development and differentiation is incompletely understood, and comparatively little is known about the signal transduction mechanisms that are involved in this process. Since protein phosphorylation in general, and tyrosine phosphorylation in particular, are known to play important roles in the regulation of a wide variety of cellular processes, particularly in the control of gene expression and the relaying of signals from the environment, it is likely that they play key roles in the development process as well. This proposal seeks to investigate the role of PRL- l, a recently-identified nuclear protein tyrosine phosphatase of novel type, in the processes of intestinal development and differentiation. We have recently learned that despite PRL- 1's induction pattern in association with the growth response in regenerating liver and fibroblasts, it appears to display a different phenotype of expression in the intestine. Specifically, PRL-l is expressed in association with differentiation in the intestinal epithelium, but is not expressed in association with proliferation. PRL-l has also been found to be significantly expressed at several time points during gut development, including early points prior to the evolution of the crypt/villus mature epithelial architecture. In addition, we have found that in immunofluorescence experiments PRL-l displays a speckled distribution in the nucleus, and despite being readily soluble when expressed in bacteria, PRL- l is found to be associated with the insoluble fraction of the nucleus. This suggests it may be complexed with the nuclear matrix. Our goals in this project are to characterize PRL-l's role in intestinal development, test its specific role in bringing about Caco-2 colonic carcinoma cell differentiation, and ascertain PRL-l's specific sub-nuclear localization, which may help us to increase our knowledge about its cellular function, and allow us to apply this information toward better understanding how PRL-l may influence the intestinal development and differentiation processes.